1. Field of the Invention
The present invention relates generally to a network sharing (NS) system. In particular, the present invention relates to a method and apparatus for allowing a user equipment (UE) to determine validity of broadcast system information before receiving the system information.
2. Description of the Related Art
A mobile communication system includes radio access networks (RANs) and user equipments (UEs). Each of the RANs includes Node Bs (or base stations), and is connected to another network via a core network (CN). RANs that use different radio access technologies or are managed by different CN operators can be connected to a plurality of CNs managed by the same CN operator or different CN operators. Herein, a technique in which different CN operators share an RAN with each other is called “network sharing (NS).”
Specifically, an RAN for a cellular mobile communication system that follows the 3rd Generation Partnership Project 2 (3GPP2) standard (the content of the standard are hereby incorporated by reference) and uses a Code Division Multiple Access (CDMA) technology, includes a base transceiver subsystem (BTS) and a base station controller (BSC), and is connected to a CN via a mobile switching center (MSC). In another case, an RAN for a Wideband CDMA (WCDMA) system, that is a Universal Mobile Telecommunications System (UMTS) system that follows the 3GPP standard and is based on Global System for Mobile Communications (GSM) and General Packet Radio Service (GPRS), includes a cell, a Node B and a radio network controller (RNC), and is connected to a CN that includes a Serving GPRS Support Node (SGSN).
The CN operators are identified with Public Land Mobile Network (PLMN) identities (PLMN ids), and the PLMN id is created with a combination of a Mobile Country Code (MCC) and a Mobile Network Code (MNC). A UE selects a PLMN indicating an appropriate CN operator under the control of the network or spontaneously. In order to access the selected CN operator, the UE reports a PLMN identity indicating the selected PLMN to the RAN.
FIG. 1 is a diagram illustrating an NS configuration in which different CN operators share a RAN with each other.
An RAN 120 covering a cell 122, which is a specific service area, includes an RNC or a BSC and is connected to CN nodes 112, 114 and 116, each of which includes an MSC or an SGSN, via an Iu interface and/or A/Gb interface.
Different CN operators A 102, B 104 and C 106 share the CN nodes (MSC/SGSN) 112, 114 and 116, and the RAN 120 belongs to a CN operator X and is shared by the CN operators A 102, B 104 and C 106. The shared RAN 120 transmits PLMN ids, i.e., a multiple PLMN list, indicating the CN operators A 102, B 104 and C 106 that share the cell 122, as well as the CN operator X belonging to the cell 122, using system information that is broadcast to a UE 130 through a broadcast control channel (BCCH) exiting in the cell 122. The UE 130 selects an appropriate PLMN id based on the system information or by an Access Stratum (AS) layer or a Non-Access Stratum (NAS) layer. The AS layer covers a protocol related to a Uu interface between the RNC and the UE, and the NAS layer, which is an upper layer of the AS layer, covers a protocol related to an interface between the UE and the CN.
The UE 130 communicates with the RAN 120 using a radio resource control (RRC) protocol, and the term “RRC message” as used herein refers to a message exchanged between the UE 130 and the RAN 120.
The typical 3GPP system broadcasts the commonly required information to UEs in the cell, and the information broadcast over a common channel is called “system information.” Commonly, a UE updates the system information when it enters a new cell or enters a new PLMN area. However, in the NS system, the new cell the UE enters may be shared by a plurality of CN operators. In this case, the UE may perform an unnecessary operation of receiving system information in the new cell, even though the new cell uses the same system information as that of the previous cell.